The impact of model predictive control structures and constraints on a wave energy converter with hydraulic power take off system

Ocean waves present a promising renewable energy source, but are challenging to harness given their irregular nature. In order to maximize energy capture on wave energy converters (WECs), power take off (PTO) systems are typically used to effectively adjust the device's resonant frequency. Optimal control techniques can oversee the PTO operation to maximize overall power output, but optimization in real-time poses difficulties given the wave variability and underlying constraints of the system. This study compares two different model predictive control approaches. One method uses only a model of the hydrodynamics of the WEC while the second has a state space model that includes the WEC hydrodynamics as the dynamics of a hydraulic PTO system. The impact of the PTO constraints, control structure and control prediction horizon on the wave energy converter control performance was explored and quantified for irregular wave conditions. Results show that utilizing a model that includes both the hydrodynamics and PTO dynamics can increase power output by 23% compared to an approach that uses the hydrodynamics only.